Say that you have a personal loan of $2,500. You've agreed to pay $150 a month and 5 percent annual interest. How long would it take to pay off that loan? You could find out by using the NPER function, which calculates the number of payments using regular, identical payment amounts and an unchanging interest rate. You would type:

**=NPER(5%/12,-150,2500)**

Two of the arguments are familiar. This time, however, the amount of the payments is known, and the number of payments is the result you're seeking.

**interest**** rate** of 5 percent annually is divided by 12 to give the monthly rate.

**payment** amount each month is -150. (The minus sign causes this amount to be calculated as a payment.)

**present**** value** is the starting amount of the loan before interest, entered as 2500.

You would be able to pay off the loan in 17 months and a few days. The precise number is 17.3096.